In the prior art, when UE (user equipment) is in an RRC (radio resource control) connected state, after the UE is out of uplink synchronization, the UE releases an allocated uplink resource, for example, a PUCCH (physical uplink control channel) resource, an SRS (sounding reference signal) resource, or a semi-static PUSCH (physical uplink shared channel) resource. After the UE is out of uplink synchronization, the UE does not send any other information to a network side except a random access code. For example, the UE does not send uplink data. For another example, even if the UE receives downlink data sent by the network side, the UE does not perform uplink HARQ (hybrid automatic repeat request) feedback of the downlink data.
After the UE is out of uplink synchronization, if the UE needs to send uplink data or perform uplink HARQ feedback, the UE first needs to perform a random access process to implement uplink synchronization. Then, after implementing uplink synchronization, the UE sends the uplink data or performs uplink HARQ feedback.
For example, when uplink data arrives at the UE, because the UE is out of uplink synchronization and cannot perform uplink sending, the UE performs random access. After completing random access, the UE implements uplink synchronization, and then can send the uplink data. Likewise, after downlink data arrives at the network side, because the UE is out of uplink synchronization and cannot perform uplink sending, that is, cannot perform feedback on the downlink data, the network side triggers the UE to perform random access. After completing random access, the UE implements uplink synchronization. A network side device sends downlink data to the UE, and the UE performs uplink HARQ feedback on the received downlink data.
However, the relatively complex uplink synchronization process used by the UE in such conventional designs introduces relatively long delays and results in relatively low efficiency when uplink data is sent or an uplink HARQ feedback of downlink data is sent.